Fluorinated polymeric carbonylguanidylene and process thereof



United States Patent 3,354,216 FLUORINATED POLYMERIC CARBONYLGUA- NHDYLENE AND PROCESS THEREOF Donald R. Husted, St. Paul, and Robert J. Koshar, Lincoln Township, Washington County, Miun., assignors to Minnesota Mining and Manufacturing Company, St. Paul, Minn, a corporation of Delaware No Drawing. Filed Mar. 31, 1960, Ser. No. 19,111 3 Claims. (Cl. 260-583) This invention relates to highly fluorinated compounds of carbon and nitrogen and particularly to certain very highly fluorinated oxidizing agents containing fluorine, nitrogen and carbon, and the process for the preparation thereof.

It is well known that fluorine is the most electro-negative element and therefore is an oxidizing agent with very high potential. However, fluorine is a gas under ordinary conditions of pressure and temperature requiring rather special techniques in its manipulations, but particularly the very fact that it is a gas limits the extent to which its high oxidizing potential could otherwise be utilized for use where high energy output is required. Among such possible uses are a number of industrial processes where high oxidizing potential can extend the range of application, increase rate of output and the like. Many industrial requirements have heretofore been met in a more or less satisfactory Way using less powerful and more readily handled oxidizing agents. Bleaching of wood pulp, fabrics, flour and such materials may be mentioned among such uses. However, more active oxidizing agents would be :advantageous in such industrial uses if readily handled, permitting shorter process time, use of lower concentration, etc. Another field in which very high oxidation potentials are particularly desirable is in the field of reaction-type propellants where extreme releases of energy are necessary to achieve large thrusts. For such purposes the availability of relatively safely handled material possessing even a substantial fraction of the oxidizing capacity of fluorine but still at a high potential would be very desirable in formulating solid propellants.

It is known that the oxidizing potential of fluorine is retained to a considerable extent in NF and =NF radicals represented by the structures:

F N and but methods of synthesis of compounds containing such radicals are very severely limited and the introduction of a plurality of such radicals into a molecule has heretofore been extremely difficult if not impossible.

It is an object of this invention to provide fluorine-containing compositions having substantial oxidizing capacity. A further object is to provide highly fluorinated derivatives of guanidine containing fluorine in oxidizing configurations. A still further object is to provide oxidants having high oxidizing capacity at a high potential. Another object of the invention is to provide a process for producing the compositions of the invention. Other objects will become evident hereinafter.

In accordance with the above and other objects of this invention, it has now been found that compositions containing a plurality of NF and =NF groups are formed by direct fluorination of compounds which it is believed can be represented by the formula:

3,354,216 Patented Nov.. 21,. 1967 wherein n is a large number from about to 1000 or greater. These compounds are described by A. E. A. Werner in the Scientific Proceedings of the Royal Dublin Society, volume 24, page 199 if. for 1947 and the above structure is suggested as Well as the less probable isomeric structure represented by the formula:

No attempt is there made to name these polymeric compounds. It will be noted that the recurring units of the first structure are 1,3-diaza-2-keto-4-iminobutylene radicals which are divalent. The termination of the chains is probably as shown. This recurring unit may also be designated as a carbonyl guanidylene radical which is also divalent. No accepted name for this radical is known and it will also sometimes hereinafter be referred to by the empirical name diazylene radicals and the polymeric materials by the term polydiazylene. It will be understood that we are not limited to the structures postulated in using these names but refer specifically to polymeric materials formed by interaction of guanidine with either urea or urethane.

It has been known heretofore that guanidine itself, as well as urea, hydrazine, biuret and the like compounds when subjected to direct fluorination either are extensively cleaved and produce substantially only very lowboiling products or are very incompletely fluorinated to produce solids having no appreciable oxidizing capacity. It was therefore unexpected to find that direct fluorination of polydiazylene produces liquid and amorphous products in substantial amounts which contain from about 25 to about fluorine and have strong oxidizing power.

Thus, it is found that direct fiuorination using ele mental fluorine replaces substantially all of the hydrogen atoms contained in polydiazylene by fluorine atoms, whether these compounds are present undiluted or as a suspension in a suitable liquid inert to fluorine. It appears from what can be determined from the stoichiometry of the reaction and the analytical values obtained on the products that the reaction not only replaces substantially all of the hydrogen atoms by fluorine atoms but that in addition greater or lesser amounts of fluorine combine with the poly-diazylene by addition to the carbon-nitrogen double bonds which are present. Addition of fluorine probably also causes some cleavage of the C-N-skeletal chain of thev polymeric substances. The resultant products, which vary over certain ranges in fluorine content, are conveniently described collectively as hyperfluorinated diazylenes. The term hyperfluorinated is employed to signify that there is a high fluorine content but not necessarily theoretical saturation with fluorine and that some fragmentation may occur. There is reason to believe that not all of the double bonds present add fluorine and furthermore fluorinolysis would be expected to result in complete decomposition of the polydiazylene to produce CF COF NE, and HF. Surprisingly, the reaction stops well short of complete degradation to produce white to yellowish liquid and amorphous materials, which may be non-crystalline to sticky solids, greases, or mobile liquids, in which the fluorine content on analysis may vary from about 25 percent to about 60' percent by weight and the oxidizing capacity determined as described hereinbelow is from about 5 to about 25 milliequivalents of iodine per gram. Oxidizing capacity is determined using excess potassium iodide in aqueous acetonitrile followed by titration with standard solutions of sodium thiosulfate. The products have vapor pressures up to about 15 mm. of Hg at 78 C. to less than 50 mm. of Hg at 25 C., and are considered to comprise both volatile and unvolatile substances. The compositions of the invention are shock-sensitive, but are usually not so impact sensitive that a 2 kgm. weight falling through 0.5 inch (1.3 cm.; DT =l.3) will cause detonation although greater drops or greater weights may result in detonation. They can accordingly be manipulated using suitable precautions, and thus they are different from many known materials having high oxidative capacity which cannot safely be manipulated. It is, of course, only normally prudent to exercise considerable care under all circumstances since, when detonated, materials of such high energ content produce very violent explosions and in fact are so powerful as oxidizing agents that they can ignite many common organic substances. In no case should quantities over about 10 milligrams be detonated for testing.

In the analysis of the above hyperfluorinated products it appears that each available fluorine atom in an =NF or NF group is removed by iodide ion with a 2 electron change in valency, i.e. F=2I, and not as one might presume on an atom for atom basis. From this and from analytical results derived from analysis of the hyperfluorinated products of the invention it does not appear that all bonds have been fully saturated with fluorine and to some extent the products presumably still retain carbon-nitrogen and carbon-oxygen double bonds.

The compositions of the invention are thus seen to be amorphous, shock-sensitive compositions which contain carbon, nitrogen and fluorine, and which have an oxidizin-g capacity of from about 5 to about 25 mil-liequivalents of iodine per gram.

The preparations and properties of polydiazylenes formed from either guanidine and urea or guanidine and urethane are well known as hereinabove noted.

The hyperfiuorin-ated compositions of the invention are White to yellowish amorphous solids or semisolids, or greases or mobile liquids, at ordinary temperatures. They appear to consist of mixtures of similar compounds with somewhat different physical properties, which are separated from each other with difficulty. They contain substantially no residual hydrogen in the molecule, and, when they are solids, are insoluble in the common organic solvents, but can be dispersed in a variety of inert solvents and are generally soluble to some extent in fluorocarbon solvents. The liquid products are soluble in such solvents as methylene chloride, fluorotrichloromethane and the like. The solid materials do not melt, but decompose on heating; however, certain of the liquids may be distilled with great caution under highly reduced pressure. When mixed with substances which can be oxidized, such as an organic polymer, and ignited as by means of a squib, they burn with intense heat and the formation of large volumes of gases. When treated with water, or exposed to moisture, these fluorinated compounds may hydrolyze to a greater or less extent with a lowering or loss of their oxidizing power.

The infra-red spectrograms of the compounds of the invention, when carried out by using a mull of the compound in mineral oil, where solid products are obtained, and by using a capillary film of the liquid product pressed between sodium chloride plates, show the following recognizable major absorption peaks: 5.8 (C N which diminishes in intensity as the C =N bonds are more completely fluorinated), 7.4-8.5;1. (C-F, frequently broad, with a summit at about 8.011. diminishing in intensity and width as the numbers and types of C-F bond diminish and -11 (region with absorption assigned to NF and/or NF groups, characterized by one or more peaks).

Nuclear magnetic resonance values, determined by the method of Filipovich et al., J. Phys. Chem., 63, 761 (1959) indicate shielding values at -19.9 and 24.3 and sometimes other negative values corresponding to -NF groups.

Broadly speaking, the process of the invention is carried out by treating the carbonyl guanidylene polymers with elemental fluorine. For best results, the starting material should be substantially anhydrous, to avoid destruction of the =NF or NF groups after their formation. The process can be carried out at a temperature in the range of about l00 to +40 C. or even somewhat higher, and the fluorine is conveniently introduced under slight positive pressure, or if closed vessels are used, pressures up to 100 psi. can be used. Preferably, the fluorine is diluted with nitrogen or other inert gas such as argon or helium, or a Freon, such as dichlorodifluoromethane and the like, to give about 0.1 to 60 percent of fluorine in the gas stream. Too high a concentration is indicated by burning of the starting materials and this can be avoided by reduction of the fluorine concentration and/or lowering the reaction temperature, however, undiluted fluorine can be used, using great caution and slow addition when working with solid, finely powdered undiluted reactants. Residual fluorine should always be flushed out of the reactants and the apparatus, using dry nitrogen or the like, to avoid unpleasant and toxic exposure to fluorine as well as untoward effects owing to the strong oxidizing power of this substance. The apparatus used is preferably constructed from Monel metal or copper. The solid, in finely divided form, is placed in a suitable container, such as a boat, which may be of stainless steel or copper or spread on a sheet or plate, and is then contacted with fluorine for a period ranging from about 10 minutes to about 6 hours. Longer times are usually used with more highly diluted fluorine and for large samples. Generally speaking, once the process has gone to completion, no further fluorine reacts, so that continuation of the flow of fluorine is not deleterious; but excessive exposure to fluorine, of the order of 10 hours or more when highly concentrated fluorine is used, should be avoided to suppress the possibility of extensive fluorinalysis. Preferably, the reaction mixture is maintained at a temperature in the range of about to +40 C., and the fluorination process is continued for about 5 hours or longer for larger samples. When convenient, lower temperatures can be used and it is preferred to use temperatures not in excess of about 25 C. If desired, an inert liquid suspending medium can be used to suspend the finely divided reactant, and the fluorine gas with or without a diluent gas is then bubbled through the suspension. Thus, for example, fluorine-inert liquids such as perfluorinated hydrocarbons, e.g., perfluorooctanes, perfluorohexanes, and the like; perfluorocyclohexane; perfluorinated cyclic ethers such as perfiuorobutylfuran; perfluorinated tertiary amines such as tris-perfluoro-n-butylamine; and the like. Commercially obtainable fluorocarbons may contain an amount of material which is not inert toward fluorine, and in such cases, fluorine gas is passed through the selected fluorocarbon liquid for a time in small amounts just sufficient to render it substantially completely inert toward fluorine. When an inert diluent is employed in the process of the invention, the hyperfluorinated reaction product generally dissolves in the diluent.

In the procedure where no solvent is used, the product of the process is recovered for use by removal of the excess of fluorine gas and separation from any highly volatile fluorinated cleavage products which may be present. Where solvent is employed, any insoluble material is removed by filtration and the product is recovered by evaporation of the solvent, preferably under reduced pressure.

The following examples will more specifically illustrate the fluorinated oxidant compounds of the invention and the process for their preparation.

Example I This example illustrates the process of the invention in which no diluent is employed for the polydiazylene. This process is referred to as static bed fluorination.

The polymer of guanidine and urethane which appears on analysis to be polymeric l,3-diaza-2-keto-4-imino-butylene, herein referred to as polydiazylene is prepared as described by A. E. A. Werner in Scientific Proceedings of the Royal Dublin Society, volume 24, p. 199 (1947), and has an inherent viscosity of 0.162 in trifluoroacetic acid.

In a stainless steel boat is placed a sample of 205 mgm. of the above dry polydiazylene and the boat is placed in a 1 inch by 14 inch nickel tube having a polytetrafluoroethylene rupture disc at one end and arranged by means of a side arm, so that gases can be introduced at one end and removed at the other. A stream of dry prepurified nitrogen is forced through the tube containing the sample at about 130 ml. per minute to displace air since fluorine subsequently introduced may produce explosives with oxygen. Fluorine (commercially available, 95 percent pure) is introduced into the nitrogen stream (using Monel metal fittings) to give a concentration of 8.9 percent fluorine by volume and the stream of nitrogen and fluorine is passed over the carbonyl guanidylene polymer at about 20 C. for 3.66 hours. The volatile and entrained fluorination products are removed at the far end of the tube passed through sodium fluoride in an iron tube heated to about 90 to 105 C. to remove hydrogen fluoride and any residual materials condensed in a Pyrex glass trap cooled in a liquid air bath. At the end of 3.66 hours the flow of fluorine is stopped and that of nitrogen continued for about 30 minutes to flush through residual amounts of fluorine. The stainless steel boat contains a yellow amorphous solid. Decomposition by the procedure reported by Senkowski, Wolliski and Shafer in Analytical Chemistry, vol. 31, pp. 1574 to 1576 (1959) followed by titration with standard thorium nitrate solution using sodium Alizarin Red S as indicator shows 34.7 percent by weight of fluorine. Reaction of a sample with excess potassium iodide in acetonitrile followed by titration using standard iodometric procedures shows that the amorphous yellow hyperfluorinated diazylene has an oxidizing capacity of 14.1 milliequivalents (meq.) of iodine per gram. Shock sensitivity is determined by fall of a 2 kg. mass on a small sample on an iron anvil. It is recorded as the centimeters of drop needed to effect detonation, designated DT For this product DT 50. The minimum value is not usually determined. The fluid and liquid products formed in this reaction and entrained by the gas stream is not conveniently recovered on this scale although a trace of liquid is found in the liquid-air trap.

In other runs using 219 and 314 mgm. amounts of material with from 5.7 to 3.6 percent by volume of fluorine and for 1.87 and 4.58 hours at 22 and 70 C. all respectively, other mixtures of solid products are obtained having oxidizing capacities of 14.9 and 7.8 meq. iodine per gram respectively.

Example 2 The procedure of Example 1 is repeated employing 1101 mgm. of the same diazylene. The fluorination vessel is maintained at about -70 C. by means of solid carbon dioxide and a stream of 8.57 percent fluorine concentration is used for 5 hours at the end of which time the reactor is allowed to warm up to room temperature and the nitrogen stream is continued for 3 to 5 hours to flush through fluorine and entrain as much as possible of the more volatile products. On this larger scale an appreciable amount of material is collected in the liquid air trap as well as a substantial amount of yellowish solid remaining in the stainless steel boat. The solid material contains 32.4 percent fluorine by weight and has an oxidizing potential of 7.4 meq. iodine per gram.

The liquid in the trap designated as A is separated into fractions by connecting the trap (kept cold in liquid air) to a line passing serially through two receivers herein designated B and C. The first receiver, B, is cooled to 78 C. by a carbon dioxide-trichloroethylene bath and the second receiver, C, is cooled in liquid air. The liquid air bath surrounding the original trap, A, is removed and the contents permitted to vaporize as the temperature gradually rises to about 25 C. (room temperature). A liquid residue remains in the original trap. The less volatile portion of the vapors is condensed in receiver B, the more volatile material in receiver C. The product in C contains fragments such as CF NF COF and CO Both compositions in B and the original trap, A, are mixtures, part of the more volatile components being retained in trap A as a result of solubility in the less volatile constituents of that composition. On a run using twice this amount, the residue remaining in trap A was found to contain a liquid residue not evaporated at 46 mm. Hg and 25 C. which was found to be extremely sensitive to shock, heat and even to the light contact between a glass pipette containing some of the material and the walls of the container: all three resulting in detonation. On the basis of vapor phase chromatography using a polytrifluorochloroethylene oil as the continuous phase, nuclear magnetic resonance and infrared absorption spectroscopy, the'contents of receiver B appears to consist of a mixture of about 75 percent trifluoromethyl difluoramine (CF NF and almost about 25 percent of unknown compounds. The major constituent of the unknown compounds is designated compound H and shows the presence of -NF group by nuclear magnetic resonance and both nitrogenand carbon-to-fluorine bonds by infrared absorption spectroscopy. It is believed that compound H is the highly energetic oxidizer, bis-(difluoramino)-methylene difluoride, which can be represented by the formula: (F N) CF A- very small amount of other unidentifiable constituents are also present.

By the same methods, the contents of trap A is found to be a mixture of which about one-half is the same as the constituents of receiver B but in a different proportion and a considerable part of the balance is another compound designated as compound R which is believed to have a structure similar to compound H and may be tris(difl-uoramino)-methyl fluoride which can be represented by the formula (F N) CF. Compounds H and R appear to occur in trap A in approximately equal amounts. Smaller amounts of other substances also appear to be present. Compound R has major absorption peaks in the infrared at 7.8a (sharp; CF region) and 1041 (strong broad, NF region); and NMR peaks at about -24 (NF region) and about +l38 (C-F region), and these values substantiate the above formula. Analyses were run in the lower boling components of the mixture present in the composition in trap A. This composition is found to have an oxidizing capacity of 25 meq. iodine per gram. Ultimate analysis is known to be extremely diflicult for compounds containing NF and :NF groups and analyses of the liquid mixtures are therefore, run in triplicate.

Analysis (average of three runs): 8.9 percent C; 17.9 percent N; 54.8 percent F.

It would appear that these values, particularly for fluorine, may not be entirely reliable since about 19 percent of the composition which may in part represent oxygen content, is unaccounted for.

Estimates of molecular weights of fractions obtained in a different run, approximating compositions in B and the original trap, A, by vapor density measurements indicate values of about and over respectively.

Example 3 This example illustrates the process of the invention in which the polydiazylene is suspended in a fluorinednert liquid for fluorination.

A suspension of 750 mgm. of the above guanidineurethane polymer in 50 ml. of perfluoro octane (a mixture of perfluorinated C isomers) is placed in a Monel metal flask having standard taper connections and fitted with an inlet for gas from a mixing manifold, a thermocouple and a vent line passing to a Monel metal condenser. All leads through which fluorine gas is to pass are constructed of Monel metal and a polytrifluoromonochloroethylene rotameter tube with a Monel metal ball is employed to gauge the rate of flow. Nitrogen is passed through the suspension for a few minutes to flush oxygen from the system and fluorine is gradually introduced into the stream and the nitrogen concentration decreased during 0.5 hours until undiluted fluorine is passing through the suspension. This procedure is reversed after about 2.6 hours toward the end of the reaction to decrease the concentration of fluorine to zero so that a total of about 22.5 g. of fluorine has been passed through the suspension. The temperature is maintained at about 28 to 30 C. After flushing with nitrogen, the suspension is filtered through a sintered glass filter and a small amount of partially fluorinated guanidine-urethane polymer is recovered. The filtrate is evaporated carefully in vacuo to give an amorphous grease-like hyperfluorinated diazylene which, on analysis, is found to contain 48.5 percent F and to have an oxidizing capacity of 19.7 meq. iodine per gram. The impact sensitivity DT is less than 35 cm. It is apparent that some of the more volatile products such as those described in Example 2 above are entrained and codistilled during evaporation of the perfluoro octane solvent since after distillation this recovered solvent is found to possess an oxidizing capacity not found before use. The presence of such products is also demonstrable by vapor phase chromatography.

When the above procedure is repeated at a reaction temperature of about 47 to -35 C. and using larger amounts of fluorine at lower concentration for a longer time it is found that a greater amount of incompletely fluorinated insoluble solid is recovered and the amorphous greasy hyperfluorinated product is more shock-sensitive with somewhat higher oxidizing capacity.

Example 4 Polydiazylene is prepared by heating 18 g. of guanidine carbonate and 12 g. of urea (equimolar amounts) at 110 to 130 C. for 2.5 hours until evolution of gases (particularly ammonia) has ceased. The reaction mixture is then dissolved in an excess of percent by weight aqueous sodium hydroxide and the polymer reprecipitated by carbonation with an excess of carbon dioxide. The polymer is collected, washed thoroughly with water and dried at 100 C. for 18 hours. It is very similar in its properties to the polymer obtained in Example 2 above. Inherent viscosity is 0.158 in trifluoroacetic acid. Ultimate analysis shows the following weight percents:

27.7 percent C., 3.9 percent H., 52.4 percent N.

Example 5 The procedure of Example 3 is employed using polydiazylene of Example 4, under somewhat altered conditions. One gram of the polymer is suspended in 35 ml. of monofluorotrichloromethane at 56 C. and the gas stream is gradually enriched to 67 percent by volume of fluorine and maintained at that point so that during 1.5 hours about 15 g. of fluorine are passed into the suspension. The temperature rises to -33 C. due to the exothermic reaction. The reaction mixture is Worked up as before to give solid incompletely fluorinated polymer and an amorphous greasy hyperfluorinated diazylene having DT of less than 4 cm., an oxidizing capacity of 19.4 meq. of iodine per gram and containing about 32.9 percent by weight of fluorine on analysis.

Because of their high oxidizing capacities the hyperfluorinated products of the invention are useful in propellant compositions when combined with fuels such as lithium and boron and with an additional oxidizer such as ammonium perchlorate to consume any carbon which is present, such as that in the hyperfluorinated diazylene as well as any organic binder which is used.

What is claimed is:

1. Fluorinated polymeric carbonylguanidylene in which fluorine has replaced a suflicient number of hydrogen atoms and combined with sufficient carbon-nitrogen dou ble bonds so that the fluorine content is at least from about 25 to about percent of the total weight of the compound.

2. A highly fluorinated, shock-sensitive oxidant composition, consisting essentially of fluorinated carbon atoms and a plurality of fluorinated nitrogen atoms and containing no carbon to carbon bonds, containing at least from about 25 to about 60 percent of fluorine and produced by the direct fluorination of polymeric carbonylguanidylene.

3. A process for the production of hyperfluorinated oxidants, which comprises interreacting together at a temperature in the range of about C. to 100 C. elemental fluorine and polymeric carbonylguanidylene.

References Cited Lovelace et al., Aliphatic Fluorine Compounds, pp. 2023 (1958), Reinhold Publishing Corporation, New York. Copy in Division 6.

CHARLES B. PARKER, Primary Examiner.

R. L. CAMPBELL, Examiner.

J. W. WHISLER, B. BILLIAN, Assistant Examiners. 

1. FLUORINATED POLYMERIC CARBONYLGUANIDYLENE IN WHICH FLUORINE HAS REPLACED A SUFFICIENT NUMBER OF HYDROGEN ATOMS AND COMBINED WITH SUFFICIENT CARBON-NITROGEN DOUBLE BONDS SO THAT THE FLUORINE CONTENT IS LEAST FROM ABOUT 25 TO ABOUT 60 PERCENT OF THE TOTAL WEIGHT OF THE COMPOUND. 